Hydraulic assembly for a vehicle brake system

ABSTRACT

A hydraulic assembly for a vehicle brake system comprising at least two brake circuits and wheel brakes associated with the brake circuits. The hydraulic assembly comprises a pressure generator for generating a central hydraulic pressure for the brake circuits independently of the driver at least in the case of service braking initiated by the driver. Furthermore, at least one pressure adjusting device is provided for adjusting for each individual brake circuit the central hydraulic pressure that is generated by the pressure generator independently of the driver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/935,494, filed Nov. 9, 2015, now U.S. Pat. No. 9,783,176, issued Oct.10, 2017, the disclosures of which are incorporated herein by referencein entirety, which is a continuation of U.S. patent application Ser. No.13/696,688, filed Feb. 11, 2013, now U.S. Pat. No. 9,227,609, issuedJan. 5, 2016, the disclosures of which are incorporated herein byreference in entirety, which is the national stage of InternationalApplication No. PCT/EP2011/002320, filed May 10, 2011, the disclosuresof which are incorporated herein by reference in entirety, and whichclaimed priority to German Patent Application No. DE 10 2010 020 002.6,filed May 10, 2010, the disclosures of which are incorporated herein byreference in entirety.

BACKGROUND OF THE INVENTION

The present disclosure is directed towards a hydraulic assembly for amultiple-circuit vehicle brake system. The hydraulic assembly comprisesa pressure generator for generating a hydraulic pressure in the brakecircuits independently of the driver.

Conventional vehicle brake systems may be actuated either by a driver orindependently of a driver. A braking operation initiated by the driveris referred to also as a service braking operation. In the course of aservice braking operation initiated by the driver or independentlythereof a driving safety system may cause a braking operationindependently of the driver. This is referred to as a system brakingoperation that may be chronologically superimposed on a service brakingoperation or occur at a separate time to a service braking operation.Known driving safety systems comprise for example an anti-lock brakingsystem (ABS), electronic stability control (ESC and/or ESP) and similarsystems.

In conventional vehicle brake systems, in the case of a service brakingoperation, the hydraulic pressure in the brake circuits is generated bythe driver himself. For this purpose the brake circuits are coupledhydraulically to a master cylinder, which is actuated by the driver in aknown manner by means of a brake pedal.

In modern vehicle brake systems the generation of hydraulic pressureduring a service braking operation may be effected also by the means ofa pressure generator that is actuable independently of the driver. As arule such a pressure generator is a hydraulic pump, which is for examplepart of an electrohydraulic vehicle brake system or a regenerativevehicle brake system (“hybrid brake system”).

In an electrohydraulic brake system, according to the “brake-by-wire”principle the master cylinder during the service braking operation isfluidically uncoupled from the brake circuits. The generation ofhydraulic pressure is effected here by means of the hydraulic pump,which is triggered in dependence upon an actuating state of the brakepedal. In a regenerative vehicle brake system, during a service brakingoperation the master cylinder is likewise hydraulically uncoupled fromthe brake circuits. Decelerating of the vehicle is effected in this caseby means of a generator that charges a vehicle battery. If the driverrequires a greater vehicle deceleration than the generator can deliver,the hydraulic pump generates a supplementary hydraulic pressure in thebrake circuits. This process is referred to also as “blending”.

From DE 10 2007 047 208 A1 and corresponding U.S. Patent ApplicationPublication No. 2010/0219678 A1, both of which are incorporated byreference herein in entirety, a dual-circuit electrohydraulic brakesystem is known. The brake system comprises two electric motor-drivenpressure generators, which are realized in the form of a dual-circuitfluid feed pump. By means of the dual-circuit fluid feed pump anindividual hydraulic pressure may be generated in each of the two brakecircuits.

BRIEF SUMMARY OF THE INVENTION

A feature of the present disclosure is a vehicle brake system, whichduring a service braking operation initiated by the driver efficientlyallows a hydraulic pressure to be generated in the brake circuitsindependently of the driver. A hydraulic assembly for such a vehiclebrake system is also to be indicated.

In the present disclosure a hydraulic assembly is provided for a vehiclebrake system comprising at least two brake circuits and wheel brakesassociated with the brake circuits. The vehicle brake system comprises apressure generator for generating a central hydraulic pressure for thebrake circuits independently of the driver at least in the case of aservice braking operation. The hydraulic assembly further comprises atleast one pressure adjusting device for adjusting for each individualbrake circuit the central hydraulic pressure generated by the pressuregenerator independently of the driver.

The pressure generator may be devised to provide the central hydraulicpressure also in the case of a system braking operation. The systembraking operation may be chronologically superimposed on a servicebraking operation or occur at a separate time from a service brakingoperation. Here, by a system braking operation is generally meant abraking intervention by a driving safety system that occursindependently of the driver. The automatic braking intervention may leadfor example to a hydraulic pressure build-up or to a prevailinghydraulic pressure being raised, lowered or maintained.

The pressure generator centrally generates for all of the brake circuitsa common hydraulic pressure that may then, if necessary, be adjusted foreach individual brake circuit by means of the pressure adjuster. It isthereby possible, despite central hydraulic pressure generation, toadjust a pressure difference between the brake circuits. According to avariant the hydraulic pressure adjustment is effected across acontinuous pressure range. According to an alternative variant theadjustment relates to a discrete or even binary (“on/off”) hydraulicpressure supply of an individual brake circuit.

The pressure adjuster may comprise one or more valve devices. Each valvedevice may in turn comprise one or more valve groups, and each valvegroup may contain one or more valves. Thus, it would for example beconceivable for each valve device of the pressure adjuster to compriseone valve group comprising at least one valve per brake circuit.

Alternatively or in addition to the at least one valve device thepressure adjuster may also comprise control electronics such as forexample a control unit for the pressure generator. There may also beassociated with each valve device control electronics for actuating thevalve device. In a realization of this concept the pressure adjustercomprises a first valve device, which is electrically actuable in orderto adjust (for example reset) a hydraulic pressure corresponding to theactuating state. The first valve device may be electrically actuable bymeans of pulse width modulation. In this case the actuating state of thefirst valve device is adjustable by means of the pulse width.

An implementation of the hydraulic assembly provides that the firstvalve device comprises at least one adjusting valve, which is adjustable(at least) between an open valve position and a closed valve position.Such an adjusting valve may be adjustable digitally, discretely orcontinuously and be provided for each brake circuit.

The first valve device may further comprise a first non-return valve,which is connected in parallel to the and/or each adjusting valve. In anexemplified implementation the first non-return valve is connected inparallel to the adjusting valve in a way that in the closed state of theadjusting valve enables an overflow of the adjusting valve in thedirection of the wheel brakes. In this exemplified implementation,therefore, the non-return valve even in the closed state of theadjusting valve allows a further hydraulic pressure build-up in at leastone of the brake circuits by means of the pressure generator.

The pressure generator may comprise an inlet port for hydraulic fluid aswell as an outlet port for hydraulic fluid. These ports may be providedseparately from one another. Alternatively the ports may be realized bymeans of a single common port, via which both the intake and thedischarge of the hydraulic fluid is effected. In the latter case theports in the form of the common port are fluidically coupled to oneanother. In the former case a fluidic coupling of the two ports may beeffected within the pressure generator. Alternatively or in additionthereto, the inlet port and the outlet port may be fluidically coupledto one another also outside of the pressure generator.

In an intake line, which opens out into the inlet port, a second valvedevice may be provided. The second valve device may comprise for examplea second non-return valve, which opens in the event of an intake (forexample in the event of an intake stroke) of the pressure generator andcloses in the event of a discharge (for example in the event of adischarge stroke) of the pressure generator.

The inlet port (and/or an associated intake line) is or may be coupledto an unpressurized hydraulic fluid reservoir. From this reservoir thepressure generator may take in unpressurized hydraulic fluid before thenfeeding it into one or more of the brake circuits.

The pressure generator may comprise a hydraulic chamber for receivinghydraulic fluid so that the brake circuits may be supplied withhydraulic fluid from the hydraulic chamber. Both the inlet port and theoutlet port (and/or a corresponding combined port) may open out into thehydraulic chamber.

The pressure generator may be a conventional multi-piston pump thatgenerates a desired hydraulic pressure by means of typically a pluralityof piston strokes. According to an alternative development the pressuregenerator comprises a plunger piston that is movable within thehydraulic chamber. In an advantageous manner a single hydraulic chamberwith a single plunger piston is provided for all of the brake circuits.In the case of the pressure generator equipped with a plunger piston,given a hydraulic chamber of sufficiently large dimensions the build-upof the desired hydraulic pressure may be effected by means of a singledischarge stroke movement.

The pressure generator may comprise an electric motor for actuation ofthe piston pump and/or the plunger piston. If necessary, a gear(typically a reduction gear) may be provided between the electric motorand the pressure generator. The gear may be a belt drive, a toothed gearor a combination of these two gear types.

The electric motor may be disposed coaxially or axially offset relativeto the plunger piston. According to a realization the electric motor isprovided axially offset but paraxially relative to the plunger piston.

The pressure adjuster may further comprise a first control unit for theelectric motor. The first control unit may be devised to supply theelectric motor with trigger signals in dependence upon the hydraulicpressure to be generated. For a controlled triggering of the electricmotor a pressure sensor may further be provided (for example in thehydraulic chamber or in the brake circuits), the output signal of whichis evaluated by the first control unit for the purpose of anactual-value/setpoint-value comparison.

The hydraulic assembly may comprise a changeover device. The changeoverdevice is provided for supplying the wheel brakes selectively with thehydraulic pressure generated independently of the driver or with ahydraulic pressure generated by the driver. The changeover device may beelectrically actuable, wherein in a non-actuated state it couples thewheel brakes to a driver-actuable master cylinder and in an actuatedstate it couples the wheel brakes to the pressure generator. Thechangeover device may therefore be configured in accordance with the“push-through” principle in order for example in the event of failure ofthe pressure generator at any rate still to enable a driver-inducedhydraulic pressure generation.

With regard to the changeover device various realizations are possible.Thus, the changeover device may for example comprise a 3/2-way valve ortwo 2/2-way valves. Other valve configurations would of course also beconceivable.

The hydraulic assembly may possess a modular structure of two or moreindependently manipulable subassemblies. A plurality of technicallydifferent versions of individual subassemblies may exist. In accordancewith the modular design principle the hydraulic assembly may thereforebe configured differently for different types of vehicle.

Thus, for example the changeover device, the pressure adjuster and thepressure generator may form a first independently manipulablesubassembly (wherein the changeover device need not necessarily be partof the first subassembly). With regard to the first subassembly aplurality of different types may exist, which differ for example withregard to the hydraulic fluid feed capacity of the respective pressuregenerator and/or with regard to the configuration of the pressureadjuster. The master cylinder also may be part of the first subassemblyor part of a further subassembly.

Between the pressure adjuster and the wheel brakes a third valve devicemay be provided in order to enable braking interventions to be carriedout at the wheel brakes independently of the driver. The third valvedevice may be for example part of a driving safety system (for examplean ABS and/or ESC system).

According to a first variant the third valve device is part of the firstsubassembly. According to another variant the third valve device is partof an independently manipulable second subassembly. With regard to thesecond subassembly too, various types may exist, which differ forexample with regard to the respective valve configuration. Thus,according to a first configuration the third valve device may compriseexclusively non-controllable shut-off valves, which are switchable onlyin a binary (“on/off”) manner. According to an alternative configurationthe third valve device may comprise controllable valves (in addition oras an alternative to non-controllable shut-off valves).

In another development of the third valve device disposed between thepressure adjuster and the wheel brakes, the third valve device may beused to adjust a brake pressure for each individual wheel or wheel group(for example for a group of two wheels). The brake pressure adjustmentfor each individual wheel or wheel group may be effected in multiplexmode (for example by individual- or group opening and closing of valvesof the third valve device).

According to an implementation of the third valve device, it comprisesprecisely one valve per wheel brake. The valve may be a 2/2-way valve.There may further be provided for the third valve device controlelectronics for triggering the individual valves in multiplex mode.

Independently of the concrete form of the third valve device thepressure generator may be coupled or capable of coupling to at least onehydraulic fluid return line that is associated with the third valvedevice. The pressure generator may moreover have a fluid-receivingfunctionality for hydraulic fluid flowing back through the hydraulicfluid return line (from the wheel brakes). The second valve arrangementmay be disposed entirely or completely in the return line. Inparticular, a non-return valve of the second valve arrangement may bemounted in the return line. In this way it is possible for example toprevent hydraulic fluid that is delivered by the pressure generator frompassing through the return line to the wheel brakes.

The hydraulic fluid return line may be separate from (and also notconnectable to) an unpressurized hydraulic fluid reservoir. Thereservoir may otherwise be used for example to supply a master cylinderof the vehicle brake system with hydraulic fluid.

At least one pressure accumulator may moreover be coupled or capable ofcoupling to the hydraulic fluid return line. The at least one pressureaccumulator may be configured to store hydraulic fluid that flows backthrough the hydraulic fluid return line. The at least one pressureaccumulator may be configured as a low pressure accumulator (LPA).

According to a variant the at least one pressure accumulator is providedin the hydraulic fluid return line between the pressure generator andthe third valve device. Thus, the at least one pressure accumulator maybe introduced into the hydraulic fluid return line, say, between thesecond valve device and the third valve device. In the case of amultiple-circuit vehicle brake system a separate pressure accumulatorper brake circuit may be provided.

For carrying out braking interventions at the wheel brakes independentlyof the driver a second control unit may be provided. The second controlunit may be part of the driving safety system and be designed to triggerthe pressure generator in order in a hazardous situation to build up ahydraulic pressure independently of the driver. The second control unitmay moreover be designed to influence the prevailing hydraulic pressureby suitable triggering of the third valve device in the hazardoussituation.

According to one implementation the first control unit is part of thefirst subassembly, while the second control unit is part of the secondsubassembly. It would however also be conceivable to implement thefunctionalities of the first control unit and the second control unit ina common control unit. The common control unit may then be (like thethird valve device) part of the first subassembly.

For a regenerative vehicle brake system a third control unit may furtherbe provided for the regenerative braking mode. The third control unit isdesigned to trigger the pressure generator in the regenerative brakingmode in order to build up a hydraulic brake pressure independently ofthe driver. The build-up of the hydraulic brake pressure at the wheelbrakes may be effected during a generator mode (“blending”).

In a regenerative vehicle brake system the hydraulic assembly mayfurther comprise a pedal reaction simulation unit, which in theregenerative braking mode is actuable by means of a hydraulic pressuregenerated by the driver (for example in the master cylinder). The pedalreaction simulation unit may be part of the first subassembly.Alternatively the pedal reaction simulation unit, optionally togetherwith the master cylinder, may form an independently manipulable thirdsubassembly. Once more, various types of third subassembly may beprovided, which differ for example with regard to the volume dimensionof the master cylinder and/or of the pedal reaction simulation unit.

The presently described hydraulic assembly may be part of anelectrohydraulic or a regenerative vehicle brake system. Thecorresponding brake system may further comprise suitable devices for the“brake-by-wire” mode. Such devices may include a brake pedal withassociated pedal sensor, as well as control electronics that trigger thepressure generator in dependence upon an output signal of the pedalsensor. The respective brake system may moreover comprise the brakecircuits with associated brake lines and wheel brakes.

In the case of a regenerative vehicle brake system, in addition to thepedal reaction simulation unit a generator may further be provided. Thegenerator is used to charge a vehicle battery in the generator mode inthe course of a service braking operation.

Other advantages of this invention will become apparent to those skilledin the art from the following detailed description of the preferredembodiments, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first embodiment of a vehicle brake system;

FIGS. 2A-2C are further embodiments of a vehicle brake system;

FIG. 3 is a first embodiment of a modular structure of the vehicle brakesystem according to FIG. 1;

FIG. 4 is a second embodiment of a modular structure of the vehiclebrake system according to FIG. 1;

FIG. 5 is a third embodiment of a modular structure of the vehicle brakesystem according to FIG. 1;

FIG. 6 is a fourth embodiment of a modular structure of the vehiclebrake system according to FIG. 1;

FIG. 7 is an embodiment of a subassembly in an exploded view;

FIG. 8 is a perspective view of the subassembly according to FIG. 7;

FIG. 9 is a sectional view of the subassembly according to FIGS. 7 and8;

FIG. 10 is a perspective view of a subassembly according to FIGS. 7 and8 that is supplemented by a master cylinder and a pedal reactionsimulation unit;

FIG. 11 is a further embodiment of a vehicle brake system;

FIGS. 12-14 are additional embodiments of a vehicle brake system on thebasis of the embodiment according to FIG. 11 with “closed” fluid return;and

FIG. 15 is a further embodiment of a vehicle brake system for themultiplex mode.

DETAILED DESCRIPTION OF THE INVENTION

There now follows a description with reference to the drawings ofvarious embodiments of a vehicle brake system and a hydraulic assemblyprovided therefor. In the drawings identical elements are provided withthe same reference characters.

Although the embodiments are described in connection with an exemplifiedmotor vehicle brake system and an exemplified pressure generator, itshould be pointed out that the invention is not restricted to therealizations described here. Thus, the pressure generator may not onlyoperate in accordance with the plunger principle presented here but mayalso be configured in the form of a cyclically operating multi-pistonpump, with which a pressure accumulator may selectively be associated.The presently described concept may moreover be implemented also inbrake systems with more than two brake circuits, with a different brakecircuit split (for example a diagonal split), etc.

FIG. 1 shows a first embodiment of a vehicle brake system 100. Thevehicle brake system 100 is an electrohydraulic vehicle brake system ora regenerative vehicle brake system (or a combination thereof).

The vehicle brake system 100 according to FIG. 1 comprises a pluralityof components, which, if need be, may be configured as one or moreindependently manipulable hydraulic assemblies. Different hydraulicassemblies may be installed at mutually remote areas of a motor vehicle.

The individual hydraulic components and their functions are firstdescribed in detail below. Possible configurations of the hydrauliccomponents will then be presented in connection with independentlymanipulable subassemblies.

As represented in FIG. 1, the vehicle brake system 100 is a dual-circuitbrake system. A first brake circuit 102 is configured to supply two rearwheel brakes 106, 108 with hydraulic fluid. A second brake circuit 104performs the same task with regard to two front wheel brakes 110, 112.

Hydraulic fluid may be supplied selectively to the two brake circuits102, 104 by a driver-actuable master cylinder 114 or by an electricmotor-operable pressure generator 116. By means of the pressuregenerator 116 it is therefore possible to generate a hydraulic pressurein the two brake circuits 102, 104 independently of the driver.

A changeover device 118 is provided functionally between the wheelbrakes 106, 108, 110, 112 on the one hand and the master cylinder 114and the pressure generator 116 on the other hand. The changeover device118 in the embodiment according to FIG. 1 comprises one electricallyactuable 3/2-way valve 120, 122 per brake circuit 102, 104.

In the electrically non-actuated state the valves 120, 122 couple thewheel brakes 106, 108, 110, 112 in accordance with the “push-through”principle to the master cylinder. Thus, in the event of failure of thevehicle electrical system or the vehicle electronic system adeceleration of the vehicle may be guaranteed by means of a hydraulicpressure generated in the master cylinder 114 by the driver. In theelectrically actuated state according to FIG. 1 the two valves 120, 122couple the wheel brakes 106, 108, 110, 112 to the pressure generator116. In this case, by means of the pressure generator 116 a build-up ofhydraulic pressure in the two brake circuits 102, 104 may be effectedboth in the course of a service braking operation initiated by thedriver and in the course of a system braking operation. Possible triggerscenarios for the pressure generator 116 in the case of anelectrohydraulic and/or regenerative service braking operation aredescribed in detail later.

The master cylinder 114 is supplied with hydraulic fluid by means of anunpressurized reservoir 124. In the electrically actuated state of the3/2-way valves 120, 122—i.e. when the master cylinder 114 is uncoupledfrom the wheel brakes 106, 108, 110, 112—the hydraulic fluid removedfrom the unpressurized reservoir 124 is fed by the master cylinder 114into a pressurized reservoir 126. The pressurized reservoir 126 is apedal reaction simulator, which because of the uncoupling of the mastercylinder 114 from the wheel brakes 106, 108, 110, 112 provides thedriver with the customary reaction behaviour of a brake pedal 128actuating the master cylinder 114. The master cylinder 114 and the pedalreaction simulation unit 126 may for example have the structure knownfrom DE 199 50 862 A1. The pedal reaction simulation unit 126 is basedhere on the mechanical “cut-off” principle, according to which as aresult of the displacement of a piston of the master cylinder 114 thepedal reaction simulation function is cut in and cut out.

As is evident from FIG. 1, a fluid line 130 (combined return/intakeline) opens out into the unpressurized hydraulic fluid reservoir 124.Through the line 130 hydraulic fluid may flow from the wheel brakes 106,108, 110, 112 back into the reservoir 124. The pressure generator 116may moreover take in hydraulic fluid through this line 130. Followingthe intake operation the hydraulic fluid that is taken in is fed intothe brake circuits 102, 104 in order in the course of a service brakingoperation or system braking operation to build up a hydraulic pressurein the wheel brakes 106, 108, 110, 112.

Between the changeover device 118 and the wheel brakes 106, 108, 110,112 a valve device 132 is provided for carrying out brakinginterventions at the wheel brakes 106, 108, 110, 112 independently ofthe driver. The valve device 132 comprises two (preferablynon-controllable) shut-off valves per wheel brake, which are designed as2/2-way valves. By means of these valves it is possible to carry out ina known manner pressure build-up, pressure-maintaining and pressurereduction phases in the course of system braking operations, i.e.safety-related driver-independent braking interventions. Such brakinginterventions may comprise for example ABS control interventions or ESCcontrol interventions. As such control interventions are known as such,they are not described in greater detail here.

The brake system 100 according to FIG. 1 further comprises a pressureadjuster 134 for adjusting for each individual brake circuit thehydraulic pressure generated centrally by the pressure generator 116.The pressure adjuster 134 in the embodiment according to FIG. 1comprises control electronics 136 as well as a valve device comprisingtwo (preferably non-controllable) shut-off valves 138, 140. Asrepresented in FIG. 1, the valves 138, 140 are electrically actuablevalves, which are open (“normally open” or “NO”) in the electricallynon-actuated state. The control electronics 136 are provided primarilyfor the pressure generator 116 and moreover enable an optionaltriggering of the valves 138, 140.

As represented in FIG. 1, a non-return valve 142, 144 loaded with aspring force is connected in parallel to each of the two valves 138,140. The parallel connection of the non-return valves 142, 144 enablesin the closed valve position of the valves 138, 140 an overflow of theclosed valves 138, 140 in the direction of the wheel brakes 106, 108,110, 112. It is therefore possible even in the closed valve position ofthese valves 138, 140 to build up and/or increase a pressure at thewheel brakes 106, 108, 110, 112 by means of the pressure generator 116if the pressure generated by the pressure generator 116 exceeds a presetthreshold value. This threshold value is defined by the spring force,with which the non-return valves 142, 144 are loaded.

A closing of the two valves 138, 140 is necessary for example if in thecourse of a braking intervention carried out independently of the driver(system braking operation) a follow-up intake of hydraulic fluid by thepressure generator 116 from the unpressurized reservoir 124 becomesnecessary. The braking intervention may be an ABS- or ESC controlprocess.

There now follows a description of the structure and mode of operationof the pressure generator 116. The task of the pressure generator 116 isto generate a central (i.e. single and/or uniform) hydraulic pressurefor both brake circuits 102, 104. The adjustment of the hydraulicpressure for each individual brake circuit is then effected, asdescribed above, by means of the pressure adjuster 134 connecteddownstream of the pressure generator 116.

The pressure generator 116 comprises an electric motor 146 that istriggerable by means of the control electronics 136, a gear 148rear-mounted at the output end of the electric motor 146, as well as acylinder/piston system 160 rear-mounted at the output end of the gear148. The cylinder/piston system 160 comprises a single hydraulic chamber150, within which a plunger piston 152 is movably guided. The positionof the plunger piston 152 within the hydraulic chamber 150—and hence thehydraulic pressure inside the hydraulic chamber 150—is adjustable bymeans of the electric motor 146.

As shown in FIG. 1, the hydraulic chamber 150 has a port 154, throughwhich hydraulic fluid may be taken into the chamber 150 and dischargedfrom the chamber 150. The intake and/or discharge of hydraulic fluid iseffected by means of a reciprocating movement of the plunger piston 152.

The port 154 is fluidically coupled to the input side of each of the twovalves 138, 140 of the pressure adjuster 134. The port 154 is moreoverfluidically coupled to the return line 130 by a non-return valve 156,which is loaded with a spring force. The non-return valve 156 isdisposed in such a way that it opens in the event of an intake stroke ofthe plunger piston and closes in the event of a discharge stroke. Inthis way hydraulic fluid may be fed from the unpressurized reservoir 124into the hydraulic chamber 150 without hydraulic fluid, which has beendischarged from the hydraulic chamber 150, being able to flow backdirectly into the unpressurized reservoir 124.

A pressure sensor 158 is likewise fluidically coupled to the port 154.The pressure sensor 158 supplies an output signal to the controlelectronics 136. On the basis of this output signal the controlelectronics 136 carry out an actual-value/setpoint value comparison andon the basis of this comparison generates trigger signals for theelectric motor 136. In this way a closed control loop for the hydraulicpressure generation in the course of a service braking operation orsystem braking operation is realized.

The realization of the pressure generator 116 that is represented in theembodiment according to FIG. 1 has certain advantages over the use ofother pressure generators such as multi-piston pumps. It is for examplepossible to dispense with the pressure accumulator for hydraulic fluidthat is typically needed with conventional multi-piston pumps. Thepressure pulsations typical of multi-piston pumps are moreovereliminated since because of the dimensioning of the hydraulic chamber150 a single reciprocating movement of the plunger piston 152 isgenerally sufficient to reduce a desired hydraulic pressure. The plungerapproach proposed here is moreover particularly suitable for the rapidbuild-up (in the order of magnitude of 1000 bar/s) of a centralhydraulic pressure with subsequent adjustment of the hydraulic pressurefor each individual brake circuit.

There now follows a detailed description of the mode of operation of thevehicle brake system 100 according to FIG. 1 and the adjustment of thehydraulic pressure centrally generated by the pressure generator 116 foreach individual brake circuit by means of the two valves 136, 140 of thepressure adjuster 134.

In the event of an electrohydraulic service braking operation thecontrol electronics 136 are designed to evaluate an output signal of adisplacement- or force sensor (not shown in FIG. 1) that is associatedwith the brake pedal 128. The control electronics 136 then generate independence upon this output signal trigger signals for the pressuregenerator 116 so that the pressure generator 116 generates a hydraulicpressure in the brake circuits 102, 104. The hydraulic pressuregenerated by the pressure generator 116 in this case corresponds to thevehicle deceleration that is desired by the driver and communicated viathe brake pedal 128.

In the event of a service braking operation in the regenerative mode, atriggering of the pressure generator 116 by means of the controlelectronics 136 is effected only if the deceleration request of thedriver exceeds the vehicle deceleration achievable in the generator mode(for example in the event of a sudden re-pressing of the brake pedal 128during an already previously initiated service braking operation). Inthis situation the control electronics 136 generate trigger signals forthe pressure generator 116, which during the generator mode are gearedto the supplementary generation of a hydraulic pressure at at least twoof the wheel brakes 106, 108, 110, 112 (front axle and/or rear axle). Afirst deceleration component therefore results from the generator mode,while a second deceleration component goes back to the actuation of atleast two of the wheel brakes 106, 108, 110, 112. The controlelectronics 136 ensure that both deceleration components togethercorrespond to the deceleration value for the service braking operationthat is requested by the driver at the brake pedal 128.

As an alternative to the two scenarios described above, a triggering ofthe pressure generator 116 by means of the control electronics 136 maybe effected also in the situation of a system braking operation (andhence independently of an actuation of the brake pedal 128). In theembodiment according to FIG. 1 the hydraulic pressure generatedcentrally by the pressure generator 116 may be adjusted for eachindividual brake circuit by means of the valves 138, 140 of the pressureadjuster 134. This hydraulic pressure adjustment for each individualbrake circuit is now described in detail.

To build up a hydraulic pressure in the brake circuits 102, 104 andhence at the wheel brakes 106, 108, 110, 112, a hydraulic pressureprovided centrally by the pressure generator 116 is built up to an equalamount in both brake circuits 102, 104 independently of the position ofthe shut-off valves 138, 140—because of the non-return valves 142, 144which are connected in parallel thereto and open as soon as there is aslight pressure build-up. To maintain the pressure the two valves 138,140 are each closed so that the hydraulic pressures built up in thebrake circuits 102, 104 cannot escape. However, an increase of thesehydraulic pressures via the non-return valves 142, 144 (by an equalamount for both brake circuits 102, 104) is possible at any time. Forthis purpose the hydraulic pressure provided centrally by the pressuregenerator 116 need merely be further increased.

To reduce the pressure the hydraulic pressure provided centrally by thepressure generator 116 has to be reduced again. In this case thehydraulic pressures built up in the brake circuits 102, 104 may bereduced for each individual brake circuit (and hence also adjusted foreach individual brake circuit). If for example in the course of anintake stroke of the pressure generator 116 the valve 138 associatedwith the brake circuit 102 is opened, while the valve 140 associatedwith the brake circuit 104 remains closed, then only the hydraulicpressure in the brake circuit 102 is reduced, while the hydraulicpressure in the brake circuit 104 is maintained. As a result a hydraulicpressure difference between the two brake circuits 102, 104 arises.

During practical operation of the vehicle brake system 100, in the eventof a braking intervention initiated by the driver and/or automaticallythe adjustment of the desired hydraulic pressures and/or hydraulicpressure characteristics is effected by means of a purposeful timesequence of pressure build-up, pressure-maintaining and pressurereduction phases. For this purpose the pressure generator 116 and thevalves 138, 140 are triggered in a suitable manner by means of thecontrol electronics 136 in order, if need be, to realize a hydraulicpressure adjustment for each individual brake circuit. In the embodimentaccording to FIG. 1 the adjustment of the hydraulic pressures for eachindividual brake circuit results primarily from the fact that in thecourse of pressure reduction phases a pressure difference between thebrake circuits 102, 104 may be adjusted by individual opening of one ofthe valves 138, 140.

For an ABS control process, but also to support other driver-independentbraking interventions (for example ESP control, brake assist orregenerative braking) the third valve device 132 is available. Asalready mentioned, the third valve device 132 in a known manner allowsan adjustment of the hydraulic pressures for each individual wheel andhence of the brake pressures in the wheel brakes 106, 108, 110, 112. Inorder for example during an ABS control process to feed hydraulic fluid,which has been discharged into the unpressurized reservoir 124, backinto the brake circuits 102, 104, the associated brake circuits 102, 104by closing both valves 138, 140 are brought into a pressure-maintainingphase and the hydraulic pressure provided centrally by the pressuregenerator 116 is reduced to an extent that enables a follow-up flow ofhydraulic fluid from the unpressurized reservoir 124 through thenon-return valve 156 back into the hydraulic chamber 150 of the pressuregenerator 116. It is then possible by means of the pressure generator116 further to increase the hydraulic pressure that is maintainedbecause of the closed valves 138, 140 (by overflow of the closed valves138, 140 via the non-return valves 142, 144).

FIG. 2A shows a second embodiment of a vehicle brake system 100. Thevehicle brake system according to FIG. 2A largely corresponds to thevehicle brake system of the first embodiment. For this reason only thestructural features that differ are described in detail below. Thedifferences relate primarily to the configuration of the pedal reactionsimulation unit 126, the changeover device 118 and the pressure adjuster134.

The pedal reaction simulation unit 126 has been modified to the extentthat the simulation functionality is now cut in and cut out by means ofan electromagnetically actuated 2/2-way valve. A possible realization ofthe thus configured pedal simulation unit 126 is known from DE 196 38102 A1 and corresponding U.S. Pat. No. 6,135,572, the disclosures ofwhich are both incorporated by reference herein in entirety. A furtherpossible realization of the pedal reaction simulation unit 126 withexternal simulation spring is described in DE 10 2007 047 208 A1.

Both in the form of construction of the pedal reaction simulation unit126 according to FIG. 1 and in the corresponding construction in FIG. 2Athe master cylinder 114 is constructed with regard to the push-throughmode in accordance with a “twin” arrangement. This means that a separateactuating piston is associated with each of the two brake circuits 102,104, wherein the two actuating pistons are disposed parallel to oneanother. The relevant structural details of the master cylinder 114 maybe gathered from DE 10 2005 037 792 A1 and corresponding U.S. PatentApplication Publication No. 2010/0164276 A1, the disclosures of whichare both incorporated by reference herein in entirety.

As FIG. 2A reveals, the modified changeover device now comprises,instead of the two 3/2-way valves 120, 122 provided in the firstembodiment, four 2/2-way valves 120A, 122A, 120B, 122B that areapportioned to two functional units 118A, 118B of the changeover device.A first functional unit 118A comprises one electrically actuableshut-off valve 120A, 122A per brake circuit, which is open (“NO”) in theelectrically non-actuated state. The second functional unit 118Bcomprises one electrically actuable shut-off valve 120B, 122B per brakecircuit, which is closed (“normally closed” or “NC”) in the electricallyactuated state. The second functional unit 118B further comprises onenon-return valve 142, 144 per valve 120B, 122B, which is connected inparallel to the valve 120B, 122B. The mode of operation of thenon-return valves 142, 144 with regard to an overflow has already beendescribed in connection with the first embodiment.

FIG. 2A shows the basic setting of the valves 120A, 122A, 120B, 122B inthe electrically non-actuated state. This state corresponds to the“push-through” mode, in which the wheel brakes 106, 108, 110, 112 arefluidically coupled to the master cylinder 114. To couple the pressuregenerator 116 to the wheel brakes 106, 108, 110, 112 the valves 120A,122A, 120B, 122B are electrically actuated, with the result that themaster cylinder 114 is simultaneously fluidically uncoupled from thewheel brakes 106, 108, 110, 112.

Between the two functional units 118A, 118B the modified pressureadjuster 134 is provided. The pressure adjuster 134 in the embodimentaccording to FIG. 2A comprises one controllable 2/2-way valve 138A, 140Aper brake circuit 102, 104. The pressure adjuster 134 further comprisescontrol electronics 136A for triggering the two control valves 138A,140A by means of pulse width modulation. The actuating state of the twovalves 138A, 140A is therefore individually adjustable continuouslybetween a fully open valve position and a fully closed valve position bymeans of the pulse width of the trigger signals supplied to therespective valve 138A, 140A.

A non-return valve 138B, 140B is connected in parallel to each valve138A, 140A. The combination of non-return valve 138B, 140B on the onehand and control valve 138A, 140A on the other hand enables apressure-difference-based hydraulic pressure adjustment for eachindividual brake circuit, as is described in detail in DE 102 47 651 A1.The disclosure of DE 102 47 651 A1 with regard to the structure and themode of operation of the control valves 138A, 140A is herebyincorporated by reference herein in entirety.

The decisive difference between the two embodiments of FIGS. 1 and 2Arelates to the hydraulic pressure control. In the embodiment accordingto FIG. 1 a precise controlled triggering of the electric motor 146 iseffected on the basis of an actual-value/setpoint-value comparison usinga signal supplied by the pressure sensor 158. The pressure sensor 158 inthis case is connected immediately downstream of the pressure generator116. By means of the pressure adjuster 134 a hydraulic pressureadjustment for each individual brake circuit is then effected in thecourse of pressure reduction phases. In the second embodiment accordingto FIG. 2A, on the other hand, a different control concept is pursued.Here, for the hydraulic pressure control for each individual brakecircuit trigger signals are supplied to the two control valves 138A,140A for each individual brake circuit. The control electronics 136Agenerate these control signals on the basis of anactual-value/setpoint-value comparison taking into account outputsignals of pressure sensors 158A, 158B that are connected downstream ofthe valves 138A, 140A.

In contrast to the embodiment according to FIG. 1, the embodimentaccording to FIG. 2A enables a hydraulic pressure adjustment for eachindividual brake circuit also in the course of a pressure build-upphase. Thus, for example during the build-up of a central hydraulicpressure by means of the pressure generator 116 it is also possibleindependently of the position of the valves 138, 140 for the valve 120Bassociated with the brake circuit 102 to be opened and the valve 122Bassociated with the brake circuit 104 to be closed. In such a switchingstate of the valves 120B, 122B, therefore, only the hydraulic pressurein the brake circuit 102 is increased, while the hydraulic pressure inthe brake circuit 104 is maintained. The valves 120B, 122B mayaccordingly be functionally associated with the pressure adjuster 134and be triggered by the control electronics 136A.

FIG. 2B shows a third embodiment of a vehicle brake system 100. Thevehicle brake system 100 according to FIG. 2B largely corresponds to thevehicle brake system of the second embodiment. The crucial differencefrom the vehicle brake system of the second embodiment is that thevalves 138A, 140A are no longer triggered on a pressure-difference-basedprinciple. The non-return valves 138B, 140B have therefore been omitted.

FIG. 2C shows a fourth embodiment of a vehicle brake system 100. Thevehicle brake system 100 according to FIG. 2C largely corresponds to thevehicle brake system of the second embodiment. The essential differencerelates to the fact that the two shut-off valves 138A, 140A with theassociated non-return valves 138B, 140B have been omitted. In functionalterms the valves 120B, 122B therefore take over the task of the valves138, 140 (with associated non-return valves 142, 144) of FIG. 1.Compared to the embodiment according to FIG. 2B, therefore, thepossibility of being able to adjust a pressure difference between thebrake circuits 102, 104 also in the course of a pressure build-up phasehas been eliminated.

In the embodiment according to FIG. 1, for safety reasons the 3/2-wayvalves 120, 122 of the changeover device 118 have to be so designed thatin their electrically non-actuated position determined exclusivelymechanically (by spring force) a connection of the master cylinder 114to the brake circuits 102, 104 exists and a connection to the pressuregenerator 116 and the two 2/2-way valves 138, 140 is blocked. The2/2-way valves 138, 140 may therefore be designed both as valves closed(NC) in the non-actuated state and as valves open (NO) in thenon-actuated state. In the embodiment according to FIG. 2A, for safetyreasons the two 2/2-way valves 120A, 122A, by which a connection to themaster cylinder 114 is established, have to be designed as valves open(NO) in the non-actuated state. Furthermore, at least one of the twoserially connected 2/2-way valves 138, 120B, 140, 122B has to bedesigned as a valve closed (NC) in the non-actuated state in order forthe connection to the pressure generator 116 to be blocked. The sameapplies to the embodiment according to 2B, and accordingly in theembodiment according to FIG. 2C the two 2/2-way valves 120A, 122A haveto be designed as valves open (NO) in the non-actuated state and theother two 2/2-way valves 120B/138, 122B/140 have to be designed asvalves closed (NC) in the non-actuated state.

As already mentioned, the adjustment of the desired hydraulic pressuresand/or hydraulic pressure characteristics is effected by means of apurposeful time sequence of pressure build-up, pressure-maintaining andpressure reduction phases, which are realized by means of purposefultriggering of the pressure generator 116 and the respective valves 120B,122B, 138, 140, 142, 144 of the pressure adjuster 134. In principle thehydraulic pressure adjustment for each individual brake circuit isfeasible by means of “simple” valves that have only two definedswitching positions. This presupposes that a relatively preciselyadjustable central pressure generator 116 is used. In order, because ofthe outlay and the cost involved, to then find a compromise, precisecontrollable—and hence technically more complex—valves may be used,which are controllable for example proportionally and/or by means of apressure difference (cf. FIG. 2A). As a counter to this, mechanicalcomponents of the pressure generator 116, such as for example the motor146 and/or the gear 148, may be of a simpler—and hence moreeconomical—design.

There now follows a description with reference to FIGS. 3 to 6 ofvarious modular concepts for the hydraulic assembly. The hydraulicassembly is provided for a vehicle brake system according to the firstembodiment represented in FIG. 1, wherein to underpin the modularity theunit of master cylinder 114 and pedal reaction simulation unit 126presented in the second embodiment according to FIG. 2A is used. For thesake of clarity, in FIGS. 3 to 6 not all of the reference charactershave been taken over and the control electronics 136 have been omitted.

In the following embodiments the individual components of the vehiclebrake system are apportioned differently to various subassemblies. Withregard to each of the subassemblies various types may exist, whichdiffer from one another with regard to the design of the individualcomponents. In accordance with the modular principle in a first step therequired type of each subassembly may then be selected. In a next stepthe selected types are assembled to form the hydraulic assembly. Thehydraulic assembly is then mounted as a whole in the vehicle.

A first embodiment of the modular structure of a hydraulic assembly 300is represented in FIG. 3. The hydraulic assembly 300 comprises threesubassemblies 302, 304, 306. A first subassembly 302 comprises themaster cylinder 114 with associated pedal reaction simulation unit. Asecond subassembly 304 comprises the pressure generator 116, thechangeover device 118 and the pressure adjuster 134. The secondsubassembly 304 further comprises a control unit (electronic controlunit or ECU), which comprises all of the electronic components needed totrigger the pressure generator 116, the changeover device 118 and thepressure adjuster 134, such as for example the control electronics 136according to FIG. 1). A third subassembly 306 contains the valve device132 as well as a standard control unit 306A for triggering the valvedevice 132.

FIG. 4 shows a further embodiment of the modular structure of ahydraulic assembly 400. Compared to the embodiment of FIG. 3 the twosubassembly 302, 304 have been combined into a single subassembly 402. Acontrol unit 402A associated with the subassembly 402 functionallycorresponds to a large extent to the control unit 304A according to FIG.3. A second subassembly 306 is identical to the correspondingsubassembly of FIG. 3.

FIG. 5 shows a third embodiment of the modular structure of a hydraulicassembly 500. According to FIG. 5 the hydraulic assembly 500 is realizedin the form of a single subassembly 502. The subassembly 502 comprises acontrol unit 502A, which comprises the necessary electronic componentsfor triggering the pressure generator 116, the changeover device 118,the valve device 132 and the pressure adjuster 134.

FIG. 6 shows a fourth embodiment of the modular structure of a hydraulicassembly 600. The hydraulic assembly 600 according to FIG. 6 comprises afirst assembly 302 that is identical to the corresponding assembly ofFIG. 3. A second assembly 602 contains the pressure generator 116, thechangeover device 118, the valve device 132 and the pressure adjuster134. The subassembly 602 further comprises a control unit 602A forelectrically triggering the individual components of the subassembly602.

FIG. 7 shows an exploded view of the subassembly 602 according to FIG.6, and FIG. 8 shows the subassembly 602 in the final mounted state. Asis evident from these two figures, the electric motor 146 together withthe gear 148 and the cylinder/piston system 160 forms a first assemblyunit. A second assembly unit is formed by a housing block 702, whichreceives the valves and pressure sensors of the changeover device 118,the valve device 132 and the pressure adjuster 134. The valves andpressure sensors project in FIG. 7 to the right from the housing block702 in order to be contacted by the control unit 602A. For this purposethe control unit 602A is placed onto the housing block 702. Inside thehousing block 702 the fluid lines illustrated in FIG. 6 are formed.

FIG. 9 is a sectional view of the subassembly 602 according to FIGS. 7and 8. Clearly visible are the electric motor 146, the gear 148 (in theform of a belt drive) coupled to the output side of the electric motor,and a nut/spindle arrangement 162 actuated by the gear 148. Thenut/spindle arrangement 162 comprises a spindle 166 that is driven by abelt 164 of the gear 148. The spindle 166 is coupled by bearing balls168 to a nut 170 of the nut/spindle arrangement 162. A rotationalmovement of the spindle 166 brings about a translatory movement of thenut 170 in FIG. 9 either to the left or the right, depending on thedirection of rotation.

The nut 170 is coupled rigidly to the piston 152 guided in a fluid-tightmanner in the hydraulic chamber 150. A translatory movement of the nut170 therefore directly brings about a reciprocating movement of theplunger piston 152 in the hydraulic chamber 150. In the event of anintake stroke the plunger piston 152 is moved in FIG. 9 to the right,while in the event of a discharge stroke the plunger piston 152 is movedto the left.

Not visible in the sectional view according to FIG. 9 is the combinedinlet-/outlet port 154. This is provided at the end face of the housingblock 702 facing the plunger piston 152. Clearly evident from FIG. 9, onthe other hand, is the fact that the electric motor 146 is disposedparaxially relative to the plunger piston 152. This arrangement allowsthe realization of a compact overall size of the subassembly 602.

FIG. 10 shows a perspective view of the subassembly 502 of the modularconcept according to FIG. 5. The subassembly 502 comprises, in additionto the assembly units already described in connection with FIGS. 7 and8, a master cylinder 114 as well as a pedal reaction simulation unit 126(the unpressurized reservoir is not represented in FIG. 9 as it is notnecessarily part of the subassembly).

FIG. 11 shows a further embodiment of a vehicle brake system 700. Thevehicle brake system 700 according to FIG. 11 largely corresponds to thevehicle brake system of the first embodiment according to FIG. 1. Thevehicle brake system 700 therefore also comprises a driver-actuablemaster cylinder 114, a pressure generator 116 for generating a hydraulicpressure in the brake circuits independently of the driver (i.e.primarily independently of foot force), a changeover device 118, a valvedevice 132 for carrying out braking interventions independently of thedriver, and a pressure adjuster 134 (with a control device comparable tothe control electronics 136 according to FIG. 1) having thefunctionalities described above.

The fluid line 130 is formed likewise as described in connection withthe first embodiment. In this case the fluid line in FIG. 11 issubdivided into a first portion 130A and a second portion 130B. Thefirst portion 130A, starting from the unpressurized hydraulic fluidreservoir 124, branches on the one hand via the non-return valve 156 inthe direction of the hydraulic port 154 of the pressure generator 116and on the other hand via the second part 130B of the fluid line in thedirection of the valve device 132 for carrying out braking interventionsindependently of the driver. The second part 130B serves as a hydraulicfluid return line from the valve device 132 into the reservoir 124,while the first part 130A of the line 130 has both a returnfunctionality as well as an intake functionality.

In a departure from the realization according to the form ofconstruction represented in FIG. 1, the valves 138, 140 of the pressureadjuster 134 are configured as valves closed (normally closed or NC) inthe non-actuated state. Furthermore, the structure of the mastercylinder 114 (likewise provided with a pedal reaction simulator) as wellas the valve configuration thereof have been slightly modified.

In modular terms the vehicle brake system 700 according to FIG. 11comprises a single hydraulic assembly 702, which is configured as acompact unit. The electronic components needed to trigger the individualcomponents are combined in a single control unit 702A.

FIG. 12 shows a further embodiment of a vehicle brake system 800, whichlargely corresponds to the vehicle brake system 700 according to FIG.11. For this reason only the structural features that are different aredescribed in detail below.

The differences between the embodiments according to FIG. 11 on the onehand and FIG. 12 on the other hand mainly relate to the development ofthe pressure generator 116 and of the hydraulic line 130. As illustratedin FIG. 12, the hydraulic fluid return line 130B associated with thevalve device 132 is coupled downstream by the non-return valve 156 tothe hydraulic port 154 of the pressure generator 116. In this way, inthe event of a hydraulic fluid discharge (dump) from the wheel brakesthat is controlled by means of the valve device 132, the returninghydraulic fluid (given a corresponding valve position of the changeoverdevice 118 and the pressure adjuster 134) may be fed into the hydraulicchamber 150 of the pressure generator 116 without hydraulic fluid duringa feed process being able to pass through the return line 130B to thewheel brakes.

The pressure generator 116 therefore has a fluid-receiving functionalityfor hydraulic fluid flowing back through the return line 130B. For thispurpose the piston 152 may be moved in FIG. 12 to the right in order toaccommodate the volume of the hydraulic chamber 150 for receiving thehydraulic fluid flowing back through the return line 130B.

As illustrated in FIG. 12, the hydraulic fluid return line 130B isfluidically constantly separate from the unpressurized hydraulic fluidreservoir 124. Hydraulic fluid may however pass via the intake line 130Afrom the reservoir 124 in the event of a discharge stroke of the piston152 into the hydraulic chamber 150. The hydraulic chamber 150 maytherefore be filled with hydraulic fluid both from the reservoir 124(namely via the hydraulic line 130A) and from the wheel brakes (namelyvia the hydraulic line 130B).

FIG. 13 shows a further embodiment of a vehicle brake system 900, whichcorresponds substantially to the vehicle brake system 800 according toFIG. 12. The brake system 900 additionally comprises a low pressureaccumulator (LPA) 902 in the return line 130B. The pressure accumulator902 is inserted into the return line 130B between the valve device 132and the non-return valve 156. The task of the pressure accumulator 902is to store the hydraulic fluid flowing off from the wheel brakestemporarily until it may pass during an intake stroke of the piston 152into the hydraulic chamber 150 of the pressure generator 116.

In the embodiment of a vehicle brake system 1000 shown in FIG. 14 twolow pressure accumulators 902A, 902B are provided in the return line130B between the valve device 132 and the pressure generator 116. Moreprecisely, there is a separate pressure accumulator 902A, 902B for eachbrake circuit. Furthermore, a separate non-return valve 156A, 156B perpressure accumulator 902A, 902B is provided in the return line 130B.

In the forms of construction shown in FIGS. 12 to 14 the hydraulic fluiddischarged from the wheel brakes is fed, not into the unpressurizedhydraulic fluid reservoir 124, but into the hydraulic chamber 150 of thepressure generator 116. The corresponding feed process may be effecteddirectly (FIG. 12) or indirectly via one or more low pressureaccumulators (FIGS. 13 and 14). This development has the advantage thatthe hydraulic fluid fed by the pressure generator 116 does not have tobe taken in (at any rate no longer has to be completely and always takenin) first from the reservoir 124, thereby shortening the pressurebuild-up phases.

A further embodiment of a vehicle brake system 1100 is shown in FIG. 15.The vehicle brake system 1100 corresponds partially to the vehicle brakesystem 100 according to FIG. 1 and/or 700 according to FIG. 11. In adeparture from those vehicle brake systems 100, 700, the valve device132 for carrying out braking interventions at the wheel brakesindependently of the driver is replaced by a valve device 132′ foradjusting the braking pressure for each individual wheel or wheel groupin multiplex mode. The valve device 132′ may be used for brake pressureadjustment both in the course of a service braking operation and in thecourse of a system braking operation.

The valve device 132′ is disposed between the pressure adjuster 134 andthe wheel brakes 106, 108, 110, 112 and comprises precisely one valve132′A, 132′B, 132′C, 132′D per wheel brake 106, 108, 110, 112. Controlelectronics 132′E are further provided, which allow a triggering of thevalves 132′A, 132′B, 132′C, 132′D in multiplex mode. For adjusting thepressure for each individual wheel or wheel group the electric motor 146is configured as a high-dynamic actuator.

The multiplex mode is generally described in WO 2006/111393 A1 and in WO2010/091883. For this reason only one exemplified example of thisoperating mode is described below, with it being assumed that at therear wheel brakes 106, 108 as a group a brake pressure of 30 bar and atthe front wheel brakes 110, 112 as a group a brake pressure of 50 bar isto be adjusted. In this case, in the run-up to the pressure build-up thevalves of the changeover device 118 and the pressure adjuster 134 areswitched in such a way that by means of the pressure generator 116 abrake pressure may be built up at the wheel brakes 106, 108, 110, 112.

At the start of the pressure build-up phase all of the valves of thevalve device 132′ are open. Upon attainment of the first target pressureof 30 bar, first the valves 132′A, 132′B associated with the wheelbrakes 106, 108 of the rear wheels close, wherein the pressure continuesto rise. As soon as the pressure rise has reached a value of 50 bar(second target pressure), the valves 132′C, 132′D associated with thewheel brakes 110, 112 of the front wheels are also closed. The hydraulicpressure prevailing at the instant of closing of the respective valve132′A, 132′B, 132′C, 132′D at the respective wheel brake 106, 108, 110,112 is maintained (“locked in”) until the valve is opened again. Aftersaid opening, a further pressure build-up or a pressure reduction may beeffected.

In addition to the brake pressure adjustment for each individual wheelor wheel group by means of the valve device 132′ in multiplex mode, thepossibility of a pressure adjustment for each individual brake circuitby means of the pressure adjuster 134 is maintained. Use may be made ofthis possibility for example in a regenerative braking mode. For examplethere may be a desire to uncouple the wheel brakes of one vehicle axle(first brake circuit) completely from the pressure generator 116 for thegenerator mode, while at the wheel brakes of another vehicle axle(second brake circuit) brake pressure is to be built up by means of thepressure generator 116. For this purpose, the valve of the pressureadjuster 134 that is associated with the first brake circuit may beclosed and the valve associated with the second brake circuit may beopened.

As emerges from the exemplified description of the embodiments, a numberof significant advantages result from the combination of a centralhydraulic pressure generation with subsequent hydraulic pressureadjustment for each individual brake circuit. Further advantages arisefrom the different versions of the optional modular principle, accordingto which the hydraulic assembly is divided into different subassemblies.The previously described divisions of the hydraulic assembly intoindividual subassemblies are of course merely by way of example. Inother words, different divisions may also be carried out.

Further advantages emerge from the selective coupling of a fluid inputof the pressure generator to fluid outlets associated with the wheelbrakes. Furthermore, the embodiments presented here may be combined witha brake pressure adjustment for each individual wheel in multiplex mode.

In accordance with the provisions of the patent statutes, the principleand mode of operation of this invention have been explained andillustrated in its preferred embodiments. However, it must be understoodthat this invention may be practiced otherwise than as specificallyexplained and illustrated without departing from its spirit or scope.

What is claimed is:
 1. A hydraulic assembly for a vehicle brake systemcomprising at least two brake circuits and wheel brakes associated withthe brake circuits, the hydraulic assembly being realized in the form ofa single subassembly, comprising: a master cylinder for generating ahydraulic pressure by a driver; a pressure generator comprising anelectric motor, a gear and a cylinder/piston system with a hydraulicchamber and a plunger piston, a position of the plunger piston beingadjustable by means of the electric motor; and a housing block whichreceives valves and pressure sensors; wherein the electric motor isdisposed axially orthogonal relative to the master cylinder; a pedalreaction simulation unit; wherein the plunger piston is disposed axiallyorthogonal relative to the master cylinder; the hydraulic chamber of thepressure generator being configured to receive hydraulic fluid and theplunger piston being movable within the hydraulic chamber for generatinga hydraulic pressure independently of the driver, wherein the at leasttwo brake circuits can be supplied with hydraulic fluid from thehydraulic chamber; a changeover device for selectively coupling thewheel brakes to either the hydraulic pressure generated by the driver ora hydraulic pressure generated independently of the driver; wherein thechangeover device is electrically actuable and in a non-actuated statecouples the wheel brakes to a driver-actuable master cylinder and in anactuated state couples the wheel brakes to the pressure generator; thechangeover device being provided functionally between the wheel brakeson the one hand and the master cylinder and the pressure generator onthe other hand; wherein the housing block receives at least one ofvalves and pressure sensors of the changeover device; wherein the atleast one of valves and pressure sensors project on a side of thehousing block opposite to the electric motor; wherein the at least oneof valves and pressure sensors projecting on the side of the housingblock are covered and electrically contacted by a control unit; thecontrol unit being disposed on a side of the housing block opposite tothe electric motor; and a valve device provided between the changeoverdevice and the wheel brakes, the valve device being configured forbraking interventions at the wheel brakes independently of the driver.2. The hydraulic assembly according to claim 1, wherein the pedalreaction simulation unit is disposed paraxially relative to the mastercylinder.